Chapter 2: Reliability Growth Analysis (RGA) Module

2.1 RGA Analysis List

Going back to the Reliability Platform Dashboard, to access the RGA analysis list, select the My RGA Analysis on the downside of the dashboard. Also, by browsing the menu for RGA -> My RGA Analysis.

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The interface is like the LDA chart, not only in appearance but also in functioning.

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On the right side of the screen, there are 4 symbols; they are also present on the RGA chart dashboard and present the exact same functions:

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This is an explanation of their functions, following the order from left to right:

  1. Configure the dashboard to show relevant information in the list, such as name, quantity of items or creation date.

  2. Copy the dashboards list’s information so that the user can then paste it in another document of his choosing.

  3. Download a spreadsheet containing the dashboards information.

  4. Generate a .pdf archive of the dashboard at hand.

This chart will also sort the analysis as the preference of the user: by name, quantity of items, creation date, or by last update date, and this can be done by clicking on each feature, on the top side of the dashboard.

When one of those features are hidden by the user on the first button above the chart, the sorting will not be alternate immediately; however, when another feature is used as the sorting reference, the hidden feature cannot be used for sorting until it is reactivated.

2.2 RGA Settings

The RGA Settings can be accessed on the menu under RGA -> RGA Settings, and it works in a similar way to the LDA Settings. There, the user can reconfigure all the RGA Settings preference.

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In the General Settings field, the chosen set will determine which methods and other details will influence the calculations when modeling the RGA.

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For the Confidence Bounds, the only option that differs from the LDA Settings page is the one to choose a calculation method, because for RGA, a Chi-Square method is used.

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2.3 RGA – Data tab

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The Data tab inside an analysis is like the Data tab of an LDA analysis. As the interface’s logic stays the same, the user can edit the name of the analysis by clicking on its name and rewriting it and then hitting the save button at the side of the box. The RGA analysis is also created with a default item named ITEM 1, and that can be edited too.

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The Data types for RGA analysis have two applications and two system types, and only one application and one system type can be selected previously to the calculation, because they differ between each other.  On the other hand, the data could be a grouped type of data, and in that case the R4All will close the option for the system types, as there is no logic in defining it for a grouped data.

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This is an example of a Fielded Repairable System, set to a Single System. Unlike the LDA, the RGA will not accept that the data entry does not follow a growing order. In other words, the data need to be input as accumulative time. The Start Time in the single system is always 0 (beginning of event).

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Now, changing the RGA type to Fielded Repairable System using single system:

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Now, for a Fielded Repairable System with Grouped Data, the parameters are only Beta, Lambda and Eta, and the columns of the sheet will change, because it must bind a few equal items that presented the same behavior, regarding time to failure.

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When switching the Data Type to Reliability Growth, also using a Grouped Data type, the analysis sheet stays the same, but it will return a new set of parameters, such as Growth Rate, DMTBF (Demonstrated Mean Time Between Failure) and DFI (Demonstrated Failure Intensity), features of this type of data.

As for Multiple Systems, the entry becomes a little more complex. To add, select or delete a system, instead of filling the sheet with values, it must be done in the System Selection option, a text box with three icons beside it on the topside of the sheet.

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After creating all the systems required, hit Calculate button on the Data tab to open the menu for selecting which systems will be used in the modeling and analyzed.

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After creating all the systems required, hit Calculate button on the Data tab to open the menu for selecting which systems will be used in the modeling and analyzed.

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Now, to add a new system, the protocol stays the same. As for this case there is already a system with a starting time in 0, the new one can be created with another starting point. The R4All will prevent the entry of a failure time before the starting time, as it makes no sense for this type of analysis to enter items which have failed before operating.

So, all considered events must have time stamps bigger than the start time of the operation; if start time is being considered in the 50-hour mark, then there cannot be a time to event less than 50.

If the other system (the one that starts at time 0) is edited to have a different starting time, the R4All will allow it, however if all the systems are processed, the tool will generate an error message, warning that at least one system must start at the 0-mark reference.

Now, if a third system is created, and there is a need for the treatment of all these data, all needed to be done is to add all systems to the analysis list and calculate it. 

If there is now a need to evaluate the Reliability Growth of those already entered systems, they will not be affected when the user changes the Data Type for Reliability Growth. When selecting Reliability Growth with Multiple Systems, and recalculating the systems parameters, the difference is the same when done for a Single System data.

2.4 RGA – Plot tab

For an RGA, there are 5 types of plot:

  • Cumulative Number of Failures

  • Instantaneous MTBF vs. Time

  • Cumulative MTBF vs. Time

  • Instantaneous Failure Intensity vs. Time

  • Cumulative Failure Intensity vs. Time

Follows an example of a Cumulative Failure Intensity vs. Time:

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The Confidence Bounds button also lets the user customize how the bound curves are calculated, in the same way as in the LDA Plot, but with different methods.

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2.5 RGA – Overlay Plot tab

The Overlay Plot tab allows users to see more than one item in the same plot. As the RGA Overlay Plot tab works in a similar way to the LDA Overlay Plot tab, there is no need to show them again here. If more information is needed, please see chapter 2.6 (LDA – Overlay Plot tab).

2.6 RGA – Report tab

On the Report tab, the user can visualize all the plotted graphs from the item previously selected on the Data page, just like in the LDA Report. As the graphs were all shown in the Plot chapter, there is no need to show them again here. If more information is needed, please see chapter 2.7 (LDA – Report tab).

2.7 RGA – Calculator

The RGA Calculator has different options from the LDA Calculator, and it can be accessed just like its pair, by selecting the calculator icon on the top side of the page, right above the tabs. The calculator will be available for use after the calculation of the Data has been made.

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The icons on the left are the parameters which can be determined on a specific value for the systems. The acronyms on the buttons indicate which buttons calculate each parameter:

  • IMTBF (T): Instantaneous MTBF vs. Time

  • CMTBF (T): Cumulative MTBF vs. Time

  • IFI (T): Instantaneous Failure Intensity vs. Time

  • CFI (T): Cumulative Failure Intensity vs. Time

  • T (IMTBF): Inverse of IMTBF

  • T (CMTBF): Inverse of CMTBF

  • T (IFI): Inverse of IFI

  • T (CFI): Inverse of CFI

  • NOF (T): Number of Failures vs. Time

  • T (NOF): Inverse of NOF

  • Optimum Overhaul Time

The Inverse functions are for finding a time value that corresponds with a desired parameter value.

While calculating the parameters in the corresponding plots, the Confidence Bounds can be reconfigured to be shown with the calculation results. To maintain intuitive review, they follow the same pattern as in the LDA Calculator: the top bound is shown above the value calculated and the bottom bound under it.

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